How to Decipher Your Eyeglass Prescription
- Posted on: Feb 14 2021
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OK, you just had your eye exam at our new location in Suite 340 of the St. Vincent East Pavilion and now you have a prescription for eyeglasses. Of course, your best bet would be to take it right over to our optical shop right in our office where we have all the latest frames, one sure to be perfect for both your eyes and your style.
Beyond filling the prescription, most people wonder just what all of the different numbers on their prescription mean.
Well, let’s get into that.
Your prescription
OK, let’s say you just completed your exam and Dr. Wilkins or Dr. Donohue has given you the above eyeglass prescription. Let’s break it down.
- OD = Your right eye parameters
- OS = Your left eye parameters
Sphere
This indicates the amount of lens power prescribed for nearsightedness or farsightedness, measured in diopters. This is basically the strength of magnification needed to get your eyes to 20/20. If your number has a minus sign (-) you’re nearsighted; if it has a plus sign (+) you’re farsighted.
Cylinder & Axis
These are your astigmatism numbers. A Cylinder and Axis is required to correct your astigmatism. This is a little complicated, using meridians of the eye, degrees, and such. Remember that if you have astigmatism, the shape of your cornea is more oblong (think football) than the normal round shape. This creates refractive errors all over your eye. Just know that these two numbers correct for those errors. Again, a minus sign indicates correction for nearsighted astigmatism, and a plus sign corrects for farsighted astigmatism.
Add
This is the added magnifying power applied to the bottom part of multifocal lenses to correct for presbyopia. The number appearing in this section of the prescription is always a “plus” power. This is used for reading glasses, progressive lenses, and bifocals. The number is the same for both eyes.
Prism
A prism number indicates the amount of prismatic power, measured in diopters, needed to compensate for any alignment problems in your eyes. Not many eyeglass prescriptions have a prism number.
Pupillary Distance (PD)
PD is the distance between the center of one pupil (the central black dot of your eye) to the center of the other pupil, measured in millimeters.
Now you’re an eyeglass prescription expert. So, is it time to come see us at The Eye Clinic for your next eye exam (and maybe a new prescription)? Call us at (503) 297-4718 to make your appointment.
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